This invention relates to connection arrangements for electrical or electronic assemblies, and more particularly to a method for ensuring proper configuration of computer system having multiple boards.
Computers are usually constructed using a number of printed circuit boards or the like. While in some cases a system may have a number of universal type of slots (generic slots) where a variety of different circuit boards having different construction and function may be plugged into these slots, there are in most systems specific slots that can only accommodate unique circuit boards (modules or sub-systems) constructed for these specific slots, i.e., the boards are not interchangeable. Traditionally, a way of making sure the right circuit board is plugged into the right slot is by use of mechanical keying such as plugged pins, asymmetrical guide pins, etc. Such types of keying dedicates board slots to specialized functions, rendering them useless for any alternate functions. Another approach to multi-board systems is to use generic slots without mechanical keying, but this approach restricts the use of I/O pins by forcing dedication of function, or is vulnerable to damaging the circuitry on a board if improperly configured. That is, if a board is inserted into the wrong slot its circuitry may be damaged by application of voltages to the wrong conductors.
In a fault-tolerant computer system of the type set forth in copending U.S. patent application Ser. Nos. 282,469, 282,538, 282,540, 282,629, 283,139 and 283,141, filed Dec. 9, 1988, all of which are now abandoned, assigned to Tandem Computers Incorporated, each module of the system (such as a CPU, a memory module, or an I/O processor) has its own separately-controllable independent power supply. In this type of system, proper configuration of multi-board subsystems can be guaranteed by employing an electronic keying arrangement instead of a mechanical key; here the power supply to a subsystem on a board is keyed electronically to prevent power from being applied unless the configuration is correct.